Recently, accompanied with digitization of printing data, a printing plate material for CTP, which is inexpensive, can be easily handled and has a printing ability comparable with that of a PS plate, is required. Particularly, a versatile thermal processless printing plate material, which can be applied to a printing press employing a direct imaging (DI) process without development by a special developing agent and which can be treated in the same manner as in PS plates, has been required.
In a thermal processless printing plate material, an image is formed according to a recording method employing an infrared laser emitting light with infrared to near infrared wavelengths. The thermal processless printing plate material employing this recording method is divided into ablation type, heat fusible type, phase change type, and polymerization/cross-linking type.
The ablation type printing plate materials are disclosed in for example, Japanese Patent O.P.I. Publication Nos. 8-507727, 6-186750, 6-199064, 7-314934, 10-58636, and 10-244773.
These references disclose a printing plate material comprising a substrate and a hydrophilic layer or a lipophilic layer, either of which is an outermost layer. In the printing plate material having a hydrophilic layer as an outermost layer, the hydrophilic layer is imagewise exposed to imagewise ablate the hydrophilic layer, whereby the lipophilic layer is exposed to form image portions.
As the heat fusible type printing plate material, there is one comprising a hydrophilic layer or a grained aluminum plate and provided thereon, an image formation layer containing thermoplastic particles, and a water soluble binder (see, for example, Patent Publication No. 2938397). A planographic printing plate material “Thermo Lite” produced by Agfa Co., Ltd. is of this type. This type of printing plate material can form an image only by energy necessary to heat fuse, reduce energy for image formation and form an image with high speed employing a high power laser, however, has problem in providing poor strength of the formed image and poor printing durability.
As the phase change type thermal processless printing plate material, there is a printing plate material comprising a hydrophilic layer containing hydrophobic precursor particles which changes to be hydrophobic at exposed portions, the hydrophilic layer being not removed during printing (see, for example, Japanese Patent O.P.I. Publication No. 11-240270). This type of printing plate material does not change adhesion of the image formation layer and maintains strength of the image formation layer, however, requires high energy for the phase change.
As the polymerization/cross-linking type thermal processless printing plate material, there are printing plate materials as disclosed in U.S. Pat. No. 6,548,222. This type printing plate material employing a roughened surface of an aluminum support increases strength of the image formation layer due to formation of a three dimensional network structure, and exhibits high adhesion of the image formation layer to the support due to anchor effect of the layer with the increased strength, providing greatly improved printing durability.
These printing plate materials for CTP are ones providing a printing plate by image formation only due to laser exposure without development employing a specific processing agent. They can form an image, but are difficult to enhance strength of the image formation layer for high printing durability, resulting in lowering of printing durability.
In the thermal processless plate, there is no extra process such as preheating, and only one method for curing the image formation layer is substantially heat due to laser exposure.
Short exposure time and low intensity exposure are required for improving productivity of a printing plate. Long exposure time and high intensity exposure lower productivity of a printing plate and cause interference with printing operation. Accordingly, there is a limit to only laser exposure.
There has been proposed another printing plate material forming an image according to heat and Ultraviolet light radiation (see for example, Japanese Patent O.P.I. Publication Nos. 2003-98688, 2003-107682, and 2003-107751.). There are, however, no proposals solving the problems as described above.